1. Field of the Invention
The present invention relates to an automatic self-aligning roller bearing and more particularly to an automatic self-aligning roller bearing which assures a long running life and is suitably employed as a bearing usable for installations and apparatus requiring a long period of durability as well as as a bearing usable for machines and equipments requiring a high level of reliability.
2. Related Background Art
With respect to an automatic self-aligning roller bearing, a contact condition under track surfaces of the inner and outer races come in contact with a plurality of rollers at the barrel portion of the latter is not always determined from the viewpoint of elongated running life associated with rolling fatigue. For instance, in order to reduce frictional torque and temperature raising during usage for the bearing, there has been hitherto made a proposal for determining a ratio of a radius of curvature on the track surface of the inner race to a radius of curvature on the outer race as disclosed in an official gazette of Japanese Patent Publication No. 31328/1980. A purpose of the prior invention as described in the official gazette lies in that when a radius of groove on the inner race is represented by Rb, a radius of groove on the outer race is represented by Ra and a radius of each of the rollers at the barrel portion is represented by Rc, ratios of the radiuses of curvature as identified by Rc/Rb and Rc/Ra are determined in accordance with the following inequality. ##EQU1##
In the above inequality, .gamma. is equal to Da cos .alpha./dm, Da represents the maximum diameter of each of the rollers, .alpha. does a contact angle in the bearing and dm does a diameter of pitch circle of the rollers.
If the track surfaces of both the inner and outer races and the barrel portion of each of the rollers are formed so as to satisfactorily meet the above inequality, sufficient effect can be expected with respect to frictional torque and temperature raising.
However, in a case where a plurality of inner dimensions of components constituting the bearing are determined in that way, a pressure on the contact surface of one track race is not uniformly distributed as seen in the axial direction in spite of the fact that a pressure on the contact surface of the other track race is substantially uniformly distributed as seen in the axial direction. Thus, a running life of the bearing associated with rolling fatigue is determined by the track race side where a pressure on the contact surface is not uniformly distributed, resulting in a long running life as bearing being attained only with much difficulties.